1. The Field of the Invention
The subject matter of the present invention is a method of making an adherent and wipe-resistant porous SiO2-containing antireflection coating on a borosilicate glass body and a coating solution that is suitable for making the wipe-resistant antireflection coating.
2. The Related Art
It is known that porous SiO2 coatings have poor adherence on borosilicate glass bodies. That especially relates to coatings, which were made using a SiO2 sol.
To improve the adherence it has already been suggested to add tetraethyl-orthosilicate, whose dissolution products bind the SiO2 particles to each other and with the base (U.S. Pat. No. 2,601,123), to the sol. However this solution to the foregoing problem makes the manufacture complicated and comparatively expensive.
EP 0 897 898 discloses a method of using a purely aqueous coating solution, which contains the SiO2 sol and a surfactant. This method necessarily requires pre-treatment of the substrate to be coated with acetone, ethanol and water, a strongly alkaline cleaning solution (1N NaOH) or a commercial cleaning bath is necessarily required in this method. Furthermore the cleaning action during the pre-treatment must be augmented or strengthened using ultrasonic waves if necessary. These cleaning steps (see example 1) make this process expensive.
EP 1 342 702 A1 and U.S. Pat. No. 6,998,177 B2 disclose a good method, in which an alcoholic nitric acid-stabilized suspension of a SiO2 sol is used. The known poor adherence and wipe resistance of the SiO2 particle coating that is formed are avoided because H3PO4 is added to the coating liquid. The adherence and wipe resistance of the antireflection coating produced in this way is of course very good, however it has been shown that coatings of this type age in the course of several weeks. Because of this aging it becomes apparent that the original deep blue antireflection coating is fading and becoming cloudy so that the desired high transmission of incident light and the wipe resistance deteriorate. This fading can be reversed or counteracted by washing with water. It can be avoided if the glass body provided with the antireflection coating is washed with water after its manufacture while still in the factory, so that the aging problem is eliminated in practice. However these washing steps add additional effort and expense to the method.